Steering to greater flexibility: re-tool aging dedicated machines? For this plant, it makes more sense to spend a bit more to replace them with new, m
Sure, a dedicated machine delivers faster cycle times, but when it goes down, production stops until the machine is repaired. And for what it costs to re-tool that dedicated machine for another job, you can almost buy a new, more flexible, CNC machine that is better suited to today's production requirements." If you get the feeling from the above remarks that dedicated machine tools are on the way out at Visteon's Chassis plant in Indianapolis, Indiana, you're right.
The plant, which specializes in the production of power rack and pinion steering gear assemblies for passenger cars and trucks, has eliminated about half of the dial index machines used to produce input shafts, a critical component of a power steering valve. And as the input shaft jobs running on the remaining dial index machines end or change, the plant expects to retire them, rather than re-tool them, as well.
The input shaft is a cylindrical steel component, about 6 inches long by 1 inch in diameter, machined from barstock. It requires numerous operations, including an "Op 80," in which multiple holes (hydraulic fluid passages) are drilled through the OD to a main bore running the length of the part.
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At one time, the input valves were drilled almost exclusively on automatic dial index machines. Recently, however, the Visteon plant received an order for a new rack and pinion steering gear assembly with an input shaft that required an unusually small (1.5-mm diameter) hole. At a staff meeting to discuss the new job, the drill supplier advised that the small hole would have to be drilled at a higher rpm than the dial index machines were capable of, so the staff began considering alternate ways of producing the hole.
"We have a large number of dedicated machines in the plant, and there was a growing awareness that the time and cost involved in setting up the machines for different jobs greatly limited our efficiency and flexibility," explains Wahid Kapadia, a member of the Forward Models Engineering department. "We started looking for a CNC machine to drill the small hole for a number of reasons. First, many CNC machines offer the spindle speeds that we needed to drill the hole. Second, small drills are vulnerable to breakage, and CNC machines offer the tool control needed to minimize the problem.
"Third, we are very concerned about maintaining production rates," be continues. "When a problem arises on a dedicated machine, production stops and does not start again until the problem is solved. On the other hand, when production is spread over several standard CNC machine tools, if one machine develops a problem, the other machines continue to make parts, and although production is affected, it isn't completely stopped."
The plant first considered a CNC lathe with live tooling. However, it was unable to find a machine that offered the drilling speed required for the small hole.
Next, the plant looked at standard CNC drilling and tapping machines. Several such machines would be needed to satisfy the production volumes involved. However, because the machines would run in a largely unattended mode, some add-ons would be required to equip them for the job. One or more robots would be needed to automate the loading-unloading of parts. An indexing workholder would also be needed to index the input shaft in 90-degree increments for drilling. The prospect of buying the machines and fitting them with the workhandling equipment needed for the job was becoming daunting. A simpler solution was desired.
After more research, the plant investigated the A-Series machining centers made by Wasino Corp. U.S.A. (Rolling Meadows, Illinois). The A-Series consists of four-axis (X, Y, Z and C) machining centers with secondary turning capability. Configured more like automated turning machines than conventional machining centers, the series has a horizontal, 4,000-rpm spindle with a C axis that is programmable in 0.0001 inch increments. The spindle is served by a tool turret, which can accommodate a rotary or turning tool at each tool station.
The A-Series machines also feature an integral gantry loader that takes parts to be machined from, and returns machined parts to, a compact, carousel-like staging area at the rear of the machine. The machines come with chucks up to 10 inches (for the largest model) for handling discrete parts, as well as a spindle bore that permits feeding barstock or extrusions to the machine from a bar feeder.
One of the most important features of the machine to Visteon was that the tool turret could directly drive (with no gearing) rotary tools to speeds up to 10,000 rpm, providing the speed to drill the small hole needed for the new input shaft. Accordingly, the plant purchased the A-12 model (for 12 turret tools). To make certain that the plant would have adequate drilling speed for current and future jobs, it purchased the machine with a speeder head that doubled the maximum speed capability to 20,000 rpm
